1. Field of the Invention
The present invention relates to a fixed length packet switching apparatus (asynchronous transfer mode switching apparatus) which is used for building a B-ISDN (Broadband-Integrated Service Digital Network), and particularly, to an improved multi-channel packet switching apparatus which is composed of a multi-channel switch structure having a physically/logically configured multipoint-to-multipoint connection between input and output ports and is capable of preventing a cell loss and checking a lost cell.
2. Description of the Conventional Art
The technique concerning the ATM (Asynchronous Transfer Mode) which is capable of performing a transmission and exchange operation by the fixed length packet unit is important for building the B-ISDN (Broadband-Integrated Serivce Digital Network). In particular, the switching system which is one of the major systems in the communication network is implemented based on the ATM switching technique. In order to implement the above-described purposes, much study has been performed concerning the ATM switch structure. Switches which have been developed as a result of the above-described studies are currently used in the industry.
There are various ranges of speed of a link for the B-ISDN. In the B-ISDN, the information should be transmitted/received at a high speed. The basic speed of information was 155 Mbps which is the equivalent of an STM-1 (Synchronous Transfer Mode-1) and 622 Mbps which is the equivalent of an STM-4. However, 2.5 Gbps, 10 Gbps, even 100 Gbps are recently required for the high speed Gigabit Transport Network. The ATM system having a low speed of 25 Mbps, 51 Mbps, etc. may be used for Subscriber Access Network for the reason that the service network should be established at low cost. Therefore, a new switching system should have the capability of effectively adapting the above-described various channel speeds, that is multichannel switching capability.
However, the conventional switching system adapts a single channel switching method which is directed to a single-to-single interrelationship between the input and output ports for the switch network. In more detail, the single channel switching method is directed to a method wherein the output port physically and logically has one link. Therefore, the operations for allocating the bandwidth in a switch network and setting a routing path are independently implemented with respect to each port.
The multi-channel switching method is configured based on a multi-to-multi connection method between the input and output ports, and a plurality of input and output links are grouped to one link, so that the link group is logically operated as one port. Namely, since the inputted cells are provided with a routing path through one port in the group which has the same logic cells, the path setting is performed based on much opportunity, and since the total band width of a plurality of links in one logic port are shared at the maximum, it is possible to effectively use the assigned boardwidth, so that the burst characteristic of the ATM traffic is implemented.
Therefore, the system can concurrently use the input and output links, which require different speeds, through one switch network by using the above-described multi-channel switching technique. In this case, a time sharing multiplexing and demultiplexing unit which has a simple function is added to the system, whereby it is possible to configure a system which is capable of adapting various speed ranges. Therefore, it is possible to reduce the cost which is required for the system which is capable of adapting various transmission speeds.
A switching technique is disclosed for providing a few multi-channel switching functions based on the above-described demands.
Achille Pattavina disclosed a method for implementing multi-channel switching using a Batcher Banyan network in the article xe2x80x9cMulti-channel Bandwidth Allocation in a Broadband Packet Switch: IEEE JSAC, Vol. 9, Dec. 1988, pp 1489-1499xe2x80x9d. The switching apparatus which was disclosed in the above-described article is directed to using an input buffer method which checks whether a path allocation is performed and then routes a cell. Therefore, the cell loss does not occur in the switch network; however, a head-off line blocking phenomenon occurs, as a result of the input buffer method. Therefore, the cell processing capability is decreased. In addition, since there is not provided a function for preserving the sequence of cells in the switching system itself, the cell sequence should be adjusted at an end point.
Hyong S. Kim disclosed a method werein a switching apparatus is operated by a virtual FIFO (First In first Out) method in order to support a cell sequence preserving function in the article xe2x80x9cMulti-channel ATM switch with Preserved Packet Sequence: ICC 92, 1992, pp 1634-1636xe2x80x9d. This method requires an internal buffer in the switch network. In this method, it is possible to preserve the sequence of the cells; however, the buffer should be configured to have a sharing buffer type in order to reduce the capacity of the buffer, and two memory pointers are required for providing the characteristic of the FIFO, whereby the method for controlling the memory becomes complicated. In addition, since the cell storing and cell output for the memory are concurrently processed with respect to an N-number of switch input and output ports, the memory should be virtually divided into an N-number of memory spaces. Therefore, the memory control may be complicated, and the size of the switch is increased. In addition, when the port requires a high speed operation, the system becomes complicated under the condition such as memory access time.
The function for preserving the sequence of the cells from the switching system is the most important function. In particular, in the multi-channel switching method, the above-described function is considered as the more important function. Namely, when outputting the cells from one input link and the cells are divided into several input links and inputted through one virtual path to the grouped port composed of a plurality of output links, the output sequences of the cells are maintained.
However, in most conventional multi-channel switching methods, the function for preserving the output sequence of the cells is not included in the switching network. Namely, the cell to which sequence information is added is transferred to a service end point, and then the sequence of the cells are adjusted using a buffer mechanism at the service end point.
Therefore, both the end points of the service should be provided with a predetermined protocol for preserving a desired cell sequence, and such protocol should be identical at both the end points. In addition, since the sequence information is added to a payload of the cell, the transmission efficiency of the cell is decreased.
In addition, a copy function of a cell should be included in the switching network for providing a multi-casting service. Many switches among the conventional space division switches process a cell copy and a routing operation to an output port of the copied cells using an additionally provided network. Namely, a method, in which a desired number of ports is copied, and a path is designated through a routing network with respect to each of the copied cells, is used.
In order to implement the above-described method, the cell is copied to a plurality of output ports, respectively, in accordance with information with respect to a predetermined amount (the number of fanouts) for the copy, and the routing network allocates to a corresponding path in accordance with information of the final output port of a corresponding cell with respect to each cell which is divided to multiple ports and outputted.
Here, the conventional switch has a problem in that two network, namely, the copy networks and the routing network, are required for the multi-casting service, and a large capacity look-up table is required between the two networks.
In other words, the copy network performs the copy operation of the cells using digit information which should be copied, and outputs the thusly copied cells to the output port of the copy network. In this case, a fixed output port is not allocated to the cells included in one virtual path. Namely, a predetermined output port is allocated at every cell time. Therefore, a table is required for determining an output port of a routing network of a corresponding cell using predetermined information (for example, a connection identifying number which is a connection number allocated as a predetermined value in the system) included in the cell from the output port of the copy network. Namely, since it is impossible to check which copied cell is outputted to which output port, the routing table is required. In each table, the same routing path information exists in duplicate.
The entire switching system is made complicated in accordance with its operation and construction. In particular, if there are a number of virtual paths for supporting each input link, the capacity of the table should be increased. As the speed of the system input and output links is increased up to 622 Mbps and 2.5 Gbps, the number of the virtual paths for supporting the high speed operation is sharply increased. Therefore, the cost for building the system is increased, and it is difficult to configure the system which is capable of accessing the table at a high speed.
In addition, in the switching system, the cells may be lost due to an over input traffic environment. The cells which are successfully outputted from the switching apparatus in accordance with the load state of the destination device to which the output port is connected may be lost at the destination. Namely, it is possible to minimize the loss of the cells by performing flow control of proper traffic between the destinations in which the input traffic source and output traffic are received.
However, since most conventional switching apparatuses have functions for routing the cells, the function for controlling the flow of the traffic is not provided therein.
In addition, even though there is provided such traffic flow control function, cell loss may occur in the apparatus in accordance with the load of the traffic. Therefore, in view of the management of the system, it is necessary to recognize that when cell loss occurs in a predetermined input port, when the cell loss occurs it is possible to prepare a proper measurement with respect to the lost cell. However, since most commercial switching system do not have such function in the switch chip, a device should be additionally provided to the system input/output matching unit for the above-described reasons.
In the cells inputted into the switching apparatus, a destination address information is included in the routing tag, and the switching apparatus performs a self-routing operation in accordance with the information. Here, if the destination address of the routing tag is not matched with the destination address of the output ports of an actual switching apparatus for a predetermined reason, the cells inputted continuously stay in the switching apparatus, thus increasing a consumption of the resources of the apparatus. Therefore, the switching apparatus should be equipped with a function for automatically removing the error cells.
Accordingly, it is an object of the present invention to provide a multi-channel packet switching apparatus having traffic flow controlling and checking functions which overcomes the aforementioned problems encountered in the conventional art.
It is another object of the present invention to provide a multi-channel packet switching apparatus having traffic flow controlling and checking functions which is capable of allowing the input and output ports of a switch to have a multi-to-multi function, namely, a multi-channel function, thus effectively adapting an input and output link which exceed a basic speed V of the switch and is capable of increasing a service providing capability of a switching apparatus using a multi-rate function based on one switching network with respect to the links having different speeds by dynamically configuring the links by the group unit.
It is still another object of the present invention to provide a multi-channel packet switching apparatus having traffic flow controlling and checking functions which is capable of simply controlling the system and having a simpler construction by concurrently performing a cell copy function and a cell routing function for providing a multi-casting function.
It is still another object of the present invention to provide a multi-channel packet switching apparatus having traffic flow controlling and checking functions which is capable of effectively concentrating the missed cells in the case that the cells having the identical address are missed during an allocation process with respect to an output port group and minimizing the cell loss by recirculating to the routing network.
It is still another object of the present invention to provide a multi-channel packet switching apparatus having traffic flow controlling and checking functions which is capable of maintaining a multi-channel switching operation and an output sequence of the cell output during the cell recirculation.
It is still another object of the present invention to provide a multi-channel packet switching apparatus having traffic flow controlling and checking functions which is capable of maximizing the cell processing capacity of a switch by configuring a unit switch of multiple networks based on the unit switch using a multi-channel switch, simplifying a path allocation operation based on a bandwidth checking in the switching apparatus, and recognizing the bandwidth of the links connected with a predetermined terminal as one integrated bandwidth.
It is still another object of the present invention to provide a multi-channel packet switching apparatus having traffic flow controlling and checking functions which is capable of simplifying a routing of an inner pattern when integrating the switching apparatus using a 2xc3x972 switch device for a routing network and a concentrating network for providing a recirculation path and a pattern connection characteristic composed of a column and a row which are the characteristic of a crossbar network.
It is still another object of the present invention to provide a multi-channel packet switching apparatus having traffic flow controlling and checking functions which is capable of minimizing a cell loss for the entire system by detecting a cell loss in the switching apparatus and performing a flow control operation, thus increasing a cell processing efficiency.
It is still another object of the present invention to provide a multi-channel packet switching apparatus having traffic flow controlling and checking functions which is capable of automatically removing an error cell within a predetermined time, which error cell continuously occupies the source of the apparatus in a state that the error cell is not routed to an output port in accordance with an error of a routing tag.
It is still another object of the present invention to provide a multi-channel packet switching apparatus having traffic flow controlling and checking functions which is capable of supplying a traffic management of the entire system by counting the number of lost cells by the port to which the lost cells are inputted which occur due to the lack of the source of the switching apparatus under an over traffic environment and reporting a result of the supply to a system control function unit.
To achieve the above objects, there is provided an improved multi-channel packet switching apparatus having traffic flow controlling and checking functions which includes an output group address generation unit for generating an address information of a grouped output port, a routing unit for receiving a cell recirculated through a recirculation path and a newly inputted cell, allocating an output link with respect to the recirculated cell when an address by the output port inputted from the output group address generation unit and a destination address set in a routing tag of the cell inputted by the port are identical, and outputting cells, which are not applied to the output link, through a plurality of bypass links, a recirculation path setting unit for selecting cells as many as the number of recirculation paths among the cells inputted through a plurality of bypass links and outputting through the recirculation outward link, a synchronizing unit for synchronizing the cells recirculated through the recirculation link with the cells newly inputted into the routing unit based on time and providing to the routing unit, a reverse direction flow control requesting unit for counting the number of cells which are recirculated at every cell time and requesting a reverse direction flow control to a traffic providing source when the thusly counted number exceeds a threshold value, a reverse direction buffering control unit for restricting a cell output to the output port through which a request signal is outputted when a reverse direction flow control request signal is received from the traffic receiving source until the request signal is released, an error cell removing unit for removing an error cell based on the routing tag error among the cells from the bypass link by the routing unit within a predetermined time, and a cell loss counting unit for counting the cell loss which are not recirculated by the recirculation path setting unit by the input port.
Additional advantages, objects and other features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.